The field of this invention is related to the production of ethylbenzene by the catalytic dehydrogenation of cycloolefins which are present in a styrene stream.
A well-known problem in the production of styrene-butadiene rubber is a build up of vinylcyclohexene, hereinafter referred to as VHC, which causes the appreciable induction in the polymerization of butadiene and styrene, and tends to form a coagulant in the latex.
One problem with the conversion of a cycloolefin to an ethylbenzene, when the cycloolefin is in the presence of styrene, has been the polymerization of the styrene. The polymerization of styrene is a free-radical vinyl polymerization reaction, typically catalyzed by the presence of small amounts of an initiator.
Alkali metals are known initiators. The most simple initiators based on alkali metals are the free metals themselves. They are employed either in solutions or as dispersions. To create a large reaction surface, the alkali metal is coated on an inert carrier such as aluminum oxide.
Alkali metal catalyzed polymerization of styrene in hydrocarbon media and minor proportions of polar substances have been known. Such alkali metals are sodium, potassium and lithium.
VCH is formed by the thermal dimerization of unpolymerized butadiene. On a commercial scale, the amount of VCH in a styrene stream can reach 6% in the warmer months of the year.
There are many known processes for diolefin dimerization. One known process for the dimerization or codimerization of diolefin is in the liquid phase in an inert solution using a catalyst comprising a complex obtained by reacting the alkali metal or alkaline earth metal salt of a tricarbonyl nitrosyl ferrate anion with a metal halogen or pseudo halogen or complex thereof. This process operates at a temperature ranging from 20.degree. to about 120.degree. C.
Another known process teaches a liquid phase dimerization or co-dimerization of a diolefin which involves maintaining a diolefin in the solution of an inert solvent in contact with a catalyst which comprises a product of the interaction of two metal complexes, each of which is a nitrosyl and/or carbonyl ligand, wherein the interaction product contains at least one nitrosyl group. This process uses the catalyst in a liquid phase.
One known method for the production of ethylbenzene addresses those cycloolefins where the ring structure contains six carbon atoms and at least one double bond. The cycloolefins are treated at temperatures of about 20.degree. to 150.degree. C. and under pressures of about 0.8 to 2 atmospheres with an aromatization catalyst containing 5 to 25 percent by weight of an alkali metal and 75 to 95 percent by weight of aluminum oxide as the support. This method teaches that the specific surface area of the support material should generally be larger than 25 meters.sup.2 /gram, preferably larger than 100 meters.sup.2 /gram. This catalyst composition is directed to those alkali metals selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, and mixtures of the aforementioned alkali metals.